Method for producing hot-worked tellurium-containing steel article



United States Patent 3,365,922 METHUD FOR PRGDUCENG HUT-WORKED TEL-LURlUM-CQNTAlNlNG STEEL ARTICLE Robert A. (lenses, Highland, and LouisMolnar, Hammond, Ind, assignors to Inland Steel Company, Chicago, llll.,a corporation of Delaware No Drawing. Filed Feb. 1, 1965, fier. No.429,612

13 Claims. (Cl, 72-38) ABSTRACT @F THE DESCLGSURE The diminution ofsurface checking in tellurium-containing steel during hot-workingthereof by heating an unfinished form of the steel, before hot-working,in an atmosphere in which oxidizing gases, and especially water vapor,are minimized.

The present invention relates generally to methods for producinghot-worked steel articles, and more particularly to a method forproducing a hot-worked, tellurium-containing steel article underconditions which minimize surface checking of the steel article.

A steel article normally undergoes a series of hotworking operationsbetween the as-cast stage of the steel and the final marketable stage inwhich the steel is in the form of a bar, for example. Before eachhot-working operation, the steel normally undergoes a heating operationto render the steel more susceptible to deformation. For example,assuming the steel to be initially cast into ingot form, the ingot isgenerally heated in what is known as a soaking pit prior to deformationof the ingot into an intermediate stage, such as a bloom; the bloom istypically subjected to a preheating operation before it is deformed byhot-rolling into a further intermediate stage, such as a billet; and thebillet is typically subjected to a preheating operation before thebillet is deformed by hotrolling into a bar. The ingot, the bloom andthe billet are all unfinished forms of steel.

Tellurium is added to steel to increase the steels machinability. Aproblem associated with tellurium-containing steels is that these steelsare susceptible to a hotworking-caused defect reflected in checking orcracking at the surface of the steel article undergoing hot-working.

Incident to the present invention, it has been determined that thishot-Working-caused defect in tellurium-containing steels is aggravatedwhen the tellurium-containing steel is heated (prior to hot-working) inan oxidizing atmosphere, and that this is especially so when theatmosphere contains water vapor. In accordance with the presentinvention, hot-working-caused surface defects in telluriumcontainingsteels are minimized by performing the heating operation, to which thetelluriurn-containing steel is subjected prior to hot-working, in anatmosphere in which oxidizing gases are maintained at a minimum, andespecially in which water vapor (other than the immediate product ofcombustion of fuels containing hydrocarbons) is minimized to less thanthree percent and preferably less than two percent, by volume.

The method of the present invention applies to tellurium-containingcarbon and alloy steels, and the carbon or alloy steel may containeither or both of sulphur and lead as additional machinabilitydncreasingingredients. Some typical examples of tellurium-containing steels, towhich the present invention would apply, are described in Holowaty U.S.Letters Patent No. 3,152,889. Typical carbon steels to which telluriummay be added are disclosed on pages 817-18 of The Making, Shaping andTreating of Steel, United States Steel Corporation, Pittsburgh, Pa.,1957; and typical examples of alloy steels to which tellurium may beadded are disclosed on pages ICC 827-9 of the same publication. Morespecifically the invention is applicable to tellurium-containing steelshaving a base composition (i.e., Without tellurium) identified by AISINos. 1018, 1040, 1045, 1117, 1213, 12L14, 1215, 4140, 4142 and 8620.

A typical sequence of hot-working operations for reducingtellurium-containing plain carbon steel from ingot form to bar formincludes heating the ingot, in a soaking pit of conventionalconstruction, until the steel is at a temperature in the range2350-2400" F. and then subjecting the heated steel ingot to ahot-working operation to reduce the ingot to a bloom, with the steelundergoing hot-Working until the steel is typically at a temperature inthe range 2080-2120" F.

Oftentimes, before the bloom can be further reduced in cross-section, itundergoes a decrease in temperature to a temperature level below that atwhich subsequent hot-working can be performed, so that the bloom must besubjected to further heating before it can be subjected to furtherhot-deformation. Accordingly, blooms are typically subjected to areheating operation, in a reheating furnace of conventionalconstruction, until the temperature of the bloom is in the range19002200 F., following which the bloom is subjected to hot-working withthe temperature of the bloom at the time hot-working thereof is finishedbeing in excess of 1800 F.

The typical product of a hot-working operation having a bloom as itsstarting product is a billet. Before the billet is subjected to ahot-working operation, it is usually preheated, in a furnace ofconventional construction, until the billet has a temperature in therange 1900-2200 F.; and the billet is then subjected to a hot-workingoperation which produces a bar, for example, and the temperature of thebar at the finish of the hot-Working operation is in the range1750-2000" F.

The above-described heating and hot-working operations are typical formany tellurium-containing plain carbon steels, e.g., a plain carbonsteel containing up to 0.13 wt. percent carbon, 0.80-1.20 wt. percentmanganese, 0.04-0.09 Wt. percent phosphorus, 0.25-0.35 wt. percentsulphur, 0.15-0.35 wt. percent lead and 0.04-0.06 Wt. percent tellurium.Variations in heating and hot-working conditions may be necessary forparticular compositions of steels.

As previously indicated, surface defects, resulting from hot-Workingoperations of tellurium-containing steels, are aggravated by thepresence of an oxidizing gas, such as water vapor, in the atmosphere towhich the steel is subjected during any of the above-described heatingoperations. Therefore, a method in accordance with the present inventioncomprises minimizing or eliminating the oxidizing gases in the heatingatmosphere.

The optimum conditions would be to heat the tellurium-containing steelingot or bloom or billet, or Whatever the shape may be, in an inert gasatmosphere (e.g., nit-rogen or a rare gas such as argon) or in anatmosphere consisting of endothermic gases (e.g., carbon monoxide orhydrogen) and utilize electricity as the heating medium (e.g., electricradiant heating coils). The use of radiant heating coils as the sourceof heat energy eliminates one source of the oxidizing gases, H 0 and COboth of which are the product of combustion of hydrocarboncontainingfuels such as natural gas, blast furnace gas, coke oven gas, or oil, allof which are typically used to fire furnaces normally utilized in theheating of steel articles preparatory to a hot-Working operation.

In situations Where the furnaces utilized for preheating are of aconventional construction and use natural gas, oil, blast furnace gas,etc., as fuel, the presence, in the furnace atmosphere, of some 11 0resulting from combustion cannot be avoided. The H 0 content from a;combustion may be as high as 15%. Therefore, precautions shouldespecially be taken to minimize other sources of water content withinthe furnace in which the heating operation is conducted.

More specifically, in a soaking pit in which the ingot is heated, waterof condensation sometimes accumulates in the cooled-off soaking pit,between heating operations; and this water should be drained from thesoaking pit prior to the heating of the ingot. In soaking pits of theregenerative type (typical embodiments of which are illustrated at pages401-6 of The making, Shaping and Treating of Steel, supra) water willseep into the checkerboard lines through which air is passed forpreheating prior to combustion with the fuel; and steps should be takento minimize this seepage and/or to remove seepage water from the airfiues. Water may also accumulate in the fuel line leading to the soakingit, so that the fuel line should 'be drained periodically.

The same precautions described above with respect to ingot soaking pitsshould also be taken with respect to reheating furnaces for the bloomsand billets. Typical embodiments of conventional reheating furnaces aredisclosed on pages 406-11 of The Making, Shaping and Treating of Steel,supra. In billet-reheating furnaces having water-cooled skids, leaks inthe skids can be a source of water vapor in the furnace atmosphere; andmaintenance precautions should be exercised to prevent this.

Another precaution is to provide billets or blooms which are dry at thetime they are placed in the reheating furnace. Often times, the billetsor blooms are stored in outside locations where they are exposed to rainor snow, and the surface of the steel is wet at the time the reheatingfurnace is ready to receive the steel. To prevent the introduction ofwater vapor into the furnace through this medium, the billet or bloomsurfaces should be dry and this can be accomplished by storing thebillets or blooms indoors, or by subjecting the billets or blooms to adrying operation before putting them in the reheating furnaces.

Another factor to be considered in minimizing the water content withinthe reheating furnaces, is the use of wet blast furnace gas as a fuel insoaking pits or reheating furnaces. Blast furnace gas is conventionallysubjected to a wetting operation following the withdrawal of the gasfrom the blast furnace. The purpose of the wetting operation is toremove certain impurities, and this operation leaves the gassupersaturated with water vapor. There fore, the blast furnace gasshould be dried or dehumidified before utilizing it as a fuel in asoaking pit or reheating furnace. This can be accomplished, for example,by cooling the gas to condense the water vapor and reduce the H contentof the gas.

Thus, extraneous H O (i.e., H O other than that which is the immediateproduct of combustion) should be prevented from becoming a part of thefurnace atmosphere.

An optimum condition for a furnace atmosphere in whichtellurium-containing steels are heated prior to hotworking is anatmosphere devoid of water, both extraneous and the product ofcombustion. If this optimum situation cannot be obtained, the extraneouswater vapor should be kept out of the furnace atmosphere; and if this isnot entirely possible, then the extraneous water vapor content shouldpreferably be less than 2%, by volume, or, at the very most, less than3%, by volume.

Therefore, by minimizing or eliminating the water vapor and/ or otheroxidizing gases in the atmosphere of a furnace in whichtellurium-containing steel articles are reheated before hot-working,surface defects on telluriumcontaining steels will be minimized.

The present invention is also applicable to minimize similar defects inselenium-containing steels or in steels containing both tellurium andselenium, these two elements being used interchangeably in steels forthe same purpose.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A method for producing a hot-worked steel article containing at leastone ingredient selected from the group consisting of tellurium andselenium, said method comprising the steps of:

heating of an unfinished form of tellurium-containing steel, beforehot-working, within a furnace, and to a hot-working temperature;

controlling the atmosphere in said furnace to minimize oxidizing gasesin the furnace;

and then removing said unfinished form of telluriumcontaining steel fromsaid furnace and subjecting said unfinished form of steel in ahot-working operation.

2. A method as recited in claim 1 wherein the atmosphere in said furnacein a gas selected from the group consisting essentially of inert gasesand endothermic gases.

3. A method as recited in claim 2 wherein said heating is performed withradiant electric coils.

4. A method as recited in claim 1 and comprising:

heating said furnace with a combustible gas and air which produce watervapor as a product of combustion;

said atmosphere-controlling step comprising excluding extraneous watervapor from the furnace atmosphere.

5. A method as recited in claim 4 wherein the total water vapor contentof the furnace atmosphere is no greater than 15% by volume.

6. A method as recited in claim 1 and comprising:

heating said furnace with a combustible gas and air which produce watervapor as a product of combustion;

carrying said combustible gas to the furnace through a gas line;

said atmosphere-controlling step comprising removing,

before said heating step, water which has accumulated in said gas line.

7. A method as recited in claim it and comprising:

heating said furnace with a combustible gas and air which produce watervapor as a product of combustion;

passing said air through a preheating flue in a regenerativecheckerwork, on the way to said furnace;

said atmosphere-controlling step comprising removing water which hasseeped into said preheating flues.

8. A method as recited in claim it and comprising:

heating said furnace with a combustible gas and air which produce watervapor as a product of combustion;

said atmosphere-controlling step comprising removing,

before said heating step, water which has condensed within said furnace.

9. A method for producing a hot-worked steel article containing at leastone ingredient selected from the group consisting of tellurium andselenium, said method comprising the steps of:

heating an unfinished form of tellurium-containing steel, beforehot-working, within a furnace, and to a hot-working temperature;

excluding extraneous water vapor from the atmosphere of said furnace;

and then removing said unfinished form of telluriumcontaining steel fromsaid furnace and subjecting said unfinished form of steel to ahot-working operation;

whereby surface checking of the steel during hot-workis diminished.

10. A method for producing a hot-worked steel article containing atleast one ingredient selected from the group consisting of tellurium andselenium, said method comprising the steps of:

heating an unfinished form of telluriumcontaining steel, beforehot-Working, within a furnace, and to a hot'working temperature;

excluding water vapor from the atmosphere of said furnacep' and thenremoving said unfinished form of telluriumcontaining steel from saidfurnace and subjecting said unfinished form of steel to a hot-workingoperation;

whereby surface checking of the steel during hot-workis diminished.

11. A method as recited in claim ll wherein said atmosphere-controllingstep comprises:

controlling the extraneoun water vapor content of the furnace atmosphereto less than 3%, by volume.

12. A method as recited in claim 1 wherein said at- 5 References CitedUNITED STATES PATENTS 2,914,434 11/1959 Snavely 266-2 3,098,776 7/1963Elarde 148-16 3,169,857 2/1965 Rathke 75123 3,257,835 6/1966 Cofe-r eta1 7238 3,303,064 2/4967 Bernick et. a1. 14812.1

OTHER REFERENCES The Making, Shaping and Treating of Steel, US. Steel,1957, p. 414.

0 RICHARD J. HERBST, Primary Examiner.

E. M. COMBS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,365,922 January 30, 1968 Robert A. Conces et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 11, for "making" read Making line 12, for "will" read maysame line 12, for "checkerboard" read checkerwork column 4, line 15, for"in" read to column 5, line 13, for "extraneoun" read extraneous Signedand sealed this 18th day of March 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

